Biaxially oriented containers constructed of PET by either injection stretch blow molding (single stage) or reheat stretch blow molding (two stage) processes have about 80.degree. C. glass transition (Tg) temperature, about 5 cc-mil/100 in.sup.2 -24 hr-atm oxygen permeability coefficient at 30.degree. C. and 68% RH, and have found wide use in food and beverage applications that do not require hot filling. The upper use temperature of these containers can be increased by heat setting techniques to provide some hot-fill capabilities, but even when heat-set, these PET containers may have limited upper temperature uses. Thus PET has enjoyed popularity in a large number of packaging applications, but does not meet the requirements of some specific food and beverage packaging applications.
PEN has been found useful for producing monolayer biaxially oriented containers having about 1.5 cc-mil/100 in.sup.2 -24 hr-atm oxygen permeability coefficient at 30.degree. C. and 68% RH with Tg of about 125.degree. C. by either single stage or two stage processes, and these containers will be useful for a variety of food and beverage applications requiring both good barrier to oxygen (and other gases) and hot-fill capabilities.
As the markets for polyester packaging materials have developed, the needs for materials having improved performance over that offered by PET has been recognized. While it is also recognized that these needs could be filled by a material such as PEN, there are areas where some improvement over PET is desired, but the performance (and expense) of PEN is not needed or desired. These market segments could be filled by packages produced from blends of PET/PEN which would have performance levels between the two pure components. However, to be useful for most applications a packaging material would normally be clear (for some uses good clarity is a requirement), and blends of PET/PEN are generally incompatible and produce opaque parts.
Some prior information on PET/PEN blends may be found in U.S. Pat. No. 3,546,320 (1970) assigned to Sun Oil Co., U.S. Pat. No. 3,937,754 (1976) assigned to Teijin, Ltd., Japanese Patents 72/24177 (1972), 81/49014 (1981), 74/22957 (1974), and 75/74652 (1975) all assigned to Teijin, Ltd. Further information may also be found in Research Disclosures 28340 (1987) and 29410 (1988).
It has now been found that clear compatible blends containing less than 10% haze of PET/PEN can be made through the use of a compatibilizing amount of a copolyester as hereinafter disclosed, thereby avoiding a significant amount of processing and the costs associated therewith.